Conchodon infraliasicus Stoppani, 1860

Teruzzi, Giorgio, 2015, The Stoppani Collection of Large Bivalves (Bivalvia, Megalodontida) from the Upper Triassic of Lombardy, Italy, Natural History Sciences 2 (1), pp. 15-24 : 16

Conchodon infraliasicus Stoppani, 1860 -65

MSNM i28032 - Fig. 2

Conchodon infraliasicus Stoppani 1860 -1865, Tab. 38, figs. 3-5.

Plaster cast of an internal mould, painted in dark grey. The fossil was probably collected by Balsamo-Crivelli at the then Villa Frizzoni (now Villa Crella) in San Giovanni di Bellagio (CO) (Stoppani, p. 244). The original specimen, specifically designated as the type for Conchodon infraliasicus (Stoppani, p. 248) by the author, is considered lost.

MSNM i28033 - Fig. 3

Conchodon infraliasicus Stoppani 1860 -1865, Tav. 39, fig. 1.

Plaster reconstruction of a right valve. The size and ornamentation (fine concentric striae on the outer surface of the shell) match those of the specimen illustrated in T. 39, fig. 1 (Stoppani, p. 244). However, the hinges are dissimilar: in the illustration, the large front hinge tooth is globose and more irregular than that of the reconstruction, and there are two parallel cardinal teeth instead of one. Stoppani (p. 244) stated that the two cardinal teeth were a bit more prominent in the drawing, but the second tooth is not even roughly delineated in the valve reconstruction. The hinge seems to correspond more to the negative relief embossed in the plaster cast of the internal mould. A number ‘2.’ is engraved at the centre of the interior surface of the valve: what this refers to is unknown.

These differences raised doubts on whether the hinge illustrated in T. 39, fig. 1 corresponds to this plaster reconstruction. However, comparing it with the original plaster cast of the internal mould (MSNM i28032), from which the reconstruction was derived, we noticed that the grooves (in positive relief) inside the reconstructed valve perfectly matched those on the right side of the cast of the mould: these grooves (attributed by Stoppani, p. 244, to ‘ de petits dégats causés comme par des vers lithophages ’, but that most likely represent the negative imprint of tube worms encrusting the interior of the original valve) are not present on the inner face of the valve in T. 39, fig. 1, nor on the illustration of the original internal mould given in T. 38, fig. 5. Moreover, the hinge of the original mould perfectly matches that of the reconstruction. It must be assumed, therefore, that the hinges illustrated in T. 39 were ‘adapted’ by the author to show what he thought was their original appearance. In particular, the large cardinal tooth is not globose as in the reconstruction, and only one cardinal tooth is apparent. In the plaster cast of the mould, the left valve has an impression left by a possible second, not very evident, tooth (Stoppani emphasized that the two teeth in the drawing were ‘exaggerated’) and a spherical cavity that corresponds perfectly to the globose cardinal tooth. Clearly, the decisions made by Stoppani when recreating the hinge were driven by the characteristics of the traces present in the mould of the left valve. Both valves were drawn as mirror images of each other, whereas Maestri’s reconstruction matched the original conformation.

Figures

Fig.2 - MSNM i28032. Conchodon infraliasicus Stoppani, 1860-65. Plaster cast of the type; the original specimen is lost. Stoppani, 1860-65, Tav. 38, figg. 3-5. x 0.54 ca.

Fig.3 - MSNM i28033. Conchodon infraliasicus Stoppani, 1860-65. Hypothetical plaster reconstruction of a right valve. A) external view. B) internal view. Stoppani, 1860-65, Tav. 39, fig. 1. x 0.26 ca.